In micromechanical acceleration sensors, the acceleration measurement, as a rule, is based on a capacitive distance measurement between the fixed electrodes and the mobile electrode, meaning, the oscillating mass of the flexural resonator. The measurement principle is characterized, as is well known, by a high sensitivity, wherein temperature-caused measuring errors can be eliminated by inherent-compensation or self-compensation through the use of the differential measuring process and a satisfactory linearity is achieved.
The capacitance changes which depend upon the measured value are, however, very small, equally as are the gaps between the oscillating mass in the flexural resonator and the fixed electrodes, which lie in the range of a hundredth of a millimeter. Therefore, if acceleration sensors of the generic type which have an architecture which facilitates fabrication in large series, wherein the oscillating space is in connection with the outer atmosphere through recesses, are used without any protection, in particular, such as in a motor vehicle environment, then there exists the danger, due to contamination of the oscillation space, above all however through dew deposition, meaning, because of condensed or frozen moisture, of not only an impairment of the measuring accuracy, but rather also, a total failure of the acceleration sensor.
Accordingly, it is known to attach the generic acceleration sensor on a suitable carrier element together with means for a signal editing circuit and to hermetically encapsulate same in preferably a metal capsule, wherein the metal capsule is welded to the carrier in a protective gas atmosphere. This indeed creates a generator element, which can be handled and marketed without any problems, however, the fabrication effort required for this is considerable due to the manufacture of a special housing and its connecting technology, as well as, due to the insulated embedding of contact pins into the carrier and their establishing contact with the sensor or the signal editing circuit. The sealing of the acceleration sensor accomplished in this manner requires thus a plurality of fabrication steps, which fabrication steps are characterized by processes which are no longer justified in the fabrication of the sensor. Apart from that, a relatively long welding seam has to be hermetically tight and requires that there be provided, at the installation site, meaning, on a circuit board of an apparatus, the space required for the relatively large area generator element as well as assuring the contact connections.